1. Technical Field
The present invention relates to a four-stroke engine used as a power source for a portable working machine such as a coffee harvester, an olive harvester or bush cutter, which has a tool at its one end.
2. Related Art
In recent years, there is an increased demand for a working machine equipped with a four-stroke engine. Previously, a four-stroke engine was used for only a brush cutter and a backpack working machine, but recently has been widely used for, for example, a pole saw, a pole hedge trimmer, and a coffee harvester. For example, a portable four-stroke engine has been known as disclosed in Japanese Patent Application Laid-Open No. 2007-224824. In general, the part around a crankshaft needs a greater amount of oil than for a valve operating mechanism. Then, conventionally, a lubrication apparatus supplies the oil or oil mist in a crank chamber to a valve operating chamber and a valve operating mechanism, using pressure fluctuation in the crank chamber, without controlling the amount of the oil or oil mist. Therefore, the oil or oil mist is oversupplied to the valve operating chamber to lubricate the valve operating mechanism. As a result, too much oil remains in the valve operating chamber. This causes a problem that when the engine is used in different positions, oil is discharged in large quantities while blowby gas is discharged to a combustion chamber, so that oil can be consumed fast. Then, oil consumption for a short period of time causes the period of time over which oil is refilled until the next time, to be shortened, and therefore if refilling of oil is neglected, lubrication trouble may occur. In addition, if an amount of oil to be discharged further increases, unburned oil is discharged from a muffler to the outside, and this may cause environmental damage. As described above, a portable four-stroke engine has been used for various purposes, and therefore has been used in different postures.